When is tetany most likely to occur?

Tetany is a condition that is characterized by intermittent muscle spasms, which are primarily caused by a disturbance in the balance of electrolytes in the body, particularly calcium. Low levels of calcium, or hypocalcemia, can lead to increased neuromuscular excitability and can precipitate tetany as the nerves and muscles become overly responsive.

When calcium levels drop, the body's ability to stabilize and balance muscle contractions is compromised. Calcium plays a crucial role in the release of neurotransmitters and in muscle contractions, so a deficiency can lead to excessive signaling. This disruption can manifest as symptoms including muscle cramps, spasms, and the classic sign of tetany.

Other situations such as exercise, stress, or sleeping conditions can affect muscle function and may lead to muscle fatigue or cramping, but they are not direct causes of tetany in the way that low calcium levels are. Therefore, the presence of low calcium levels is specifically linked to the development of tetany, making it the correct answer.